I was able to get it to run by saying brew install mame but YMMV. The interface is still atrocious; I thought it had hard-locked my Mac (there's an experience I haven't had in 20 years) but instead it was just fullscreened on the desktop without giving me any way to get there (so only launch it from a windowed terminal).

Running the DECTALK ROM took minimal hoop-jumping. It sounds just like Stephen Hawking (so, you know, that's cool), but not "John" and "Grace".

1) Definitely not DECtalk. Have a friend in college who used a DECtalk with his laptop. Different voice. It is Bell Labs.

2) Until the internet bitrotted away they had a functional site that would have let George and Gracie say whatever you want, but it's dead now. (Thanks, Nokia!) But it has a contact for inquiries, Michael Tanenblatt, and if he is a True Geek he would be happy to hear from you. Here's his (ugh) LinkedIn: https://www.linkedin.com/in/tanenblatt/

Bell Labs had created SABLE which was an XML markup language for synthesis. Perhaps Festival (which has SABLE support) might lead to clues? Clearly Bell Labs/Lucent collaborated with CMU (http://www.speech.cs.cmu.edu/)